One type of image-reading device known in the art reads an image from an original sheet moving relative to an image reading unit in the device as the original sheet passes through a read position of the image reading unit. This type of image-reading device determines whether the leading edge or the trailing edge of the original sheet has arrived at the read position, and uses the determination results to set a read timing for the image reading unit, the size of the original image included in the read image, and the like.
One such image-reading device is disclosed in Japanese Patent Application Publication. This image-reading device includes an original-pressing plate disposed opposite the image reading unit. On the original-pressing plate is depicted an identification image, such as a pattern with colors changing in a main scanning direction, a barcode, or a special design. The image-reading device determines that the leading or the trailing edge of the original sheet is at the read position by determining whether the image data read by the image reading unit is data for the identification image or other image data.